Sexually transmitted diseases caused by Chlamydia trachomatis, an intracellular bacterial pathogen, affect approximately 90 million people worldwide. In untreated women, these infections cause serious sequelae such as pelvic inflammatory disease and ectopic pregnancy, often resulting in infertility. The long term goal of our research is to understand the mechanisms of chlamydial pathogenesis and prevent them. A vaccine to prevent such sequelae is thought to be an ideal solution to the problem, and efforts are focused on identifying of chlamydial antigens that induce a robust CD8+ T cell response, since CD8+ T cells are typically effective in clearance of intracellular pathogens. However, we have found recently that CD8+ T cells capable of producing TNF-a mediate upper genital tract (UGT) pathology, but contribute minimally to chlamydial clearance, following genital chlamydial infection in mice. TNF-a induces pleotrophic effects including apoptosis via two main receptors, TNF receptor 1 (TNFR1) and TNFR2, which have been shown to complement or oppose the effects of each other in different infection models. Therefore, the specific contributions of TNFR1 and TNFR2 in chlamydial pathogenesis need to be determined to explore therapeutic approaches in the future. We also have found that Chlamydia-specific, not nave, CD8+ T cells mediate the genital pathologies. CD8+ T cells contribute minimally to chlamydial clearance possibly due to down- regulation of MHC class I expression on Chlamydia-infected cell surfaces. Given this, it appears that Chlamydia-specific CD8+ T cells do not target infected cells efficaciously and consequently contribute minimally to chlamydial clearance; nevertheless, they get activated and cause pathology possibly by targeting uninfected cells. This suggests the possibility that chlamydial peptides are presented to CD8+ T cells by uninfected cells, but begs the question: How do uninfected cells acquire chlamydial peptides? The phenomenon of gap junction mediated antigen transport (GMAT) may explain this paradigm. GMAT occurs via channels formed by connexin (Cx) proteins, predominantly Cx43 (expressed by the gap junction alpha 1 gene, or Gja1). Connexin 43, also expressed on oviduct epithelium, has been shown to be involved in the transfer of antigenic peptides from infected to bystander uninfected cells and subsequent presentation to CD8+ T cells. Such a mechanism would explain both the pathological effects and low efficiency of chlamydial clearance mediated by this cell type. However, the role of Cx43 and GMAT in microbe-induced immunopathogenesis in vivo systems has yet to be demonstrated. Based on this, we will test our central hypothesis that CD8+ T cells mediate chlamydial reproductive pathology through TNF-a receptors and target uninfected cells. We will test this hypothesis by: Aim 1. Determine the role of TNF-a receptors in CD8+ T cell mediated chlamydial pathogenesis, and Aim 2. Determine the role of connexin 43 in CD8+ T cell mediated chlamydial pathogenesis